The important thing is what YOU think about it. Does it make you feel sexier to hear those sounds, or mocked, or amused?
If he's teasing you by imitating you, tease him back by exaggerating your own moans. You might both burst out laughing! Or afterward, ask him what he meant by it and explain that the sounds you make are involuntary and mean you are aroused.
If he's feeling as turned on as you and showing it, enjoy the togetherness. Every person shows their excitement in different ways. One of my partners said I sound like a tortoise-- please look that up on Youtube for examples :tongue:
Whatever it may be, don't forget the very best way to solve your sex questions is to Talk To Him.